1. Field of the Invention
This invention relates to a method for fabricating a semiconductor memory device, and more particularly to a method for forming an inner cylinder type storage electrode of a semiconductor memory device.
2. Description of the Related Art
With the increase of the integration degree of a semiconductor memory device, because the cell dimension and the space between cells become diminished and a capacitor should have a constant capacitance, it should demand the capacitor having a large capacitance in a narrow dimension. Recently, an inner cylinder type storage electrode is adapted so as to ensure the capacitance of a capacitor in a semiconductor memory device of above 256 mega DRAM.
FIG. 1a to FIG. 1c shows sectional views illustrating a method for forming an inner cylinder type storage electrode of a semiconductor memory device in the prior art. Referring to FIG. 1a, a first insulating layer 11 is formed on a substrate 10 and etched to form contact holes for capacitors, thereby exposing portions of the substrate 10. A conductive film 12 for storage electrode is formed over the first insulating layer 11 including the contact holes. A second insulating layer 13 is formed over the conductive film 12 to be filled in the contact holes.
Referring to FIG.1b, the second insulating layer 13 and the conductive film 12 are blanket-etched to expose the first insulating layer 11. The conductive film 12 is separated with each other to form inner cylinder type storage electrodes 12A and 12B within the contact holes.
Referring to FIG. 1c, the second insulating layer 13 and the first insulating layer 11 are wet-etched. At this time, a portion of the first insulating layer 13 which is disposed outside of the storage electrodes 12A and 12B remains by a selected thickness by controlling the etching selectivity between the first and second insulating layers 11 and 13.
With increase of the integration degree, because the area occupied by the storage electrode of the capacitor is diminished and the height of the cylinder type storage electrode becomes high, its aspect ratio is increased. Therefore, the filling property of the second insulating layer 13 which is filled in the cylinder type storage electrodes 12A and 12B becomes degraded so that the void V is occurred in the second insulating layer 13 as shown in FIG. 2. Besides, the inner portions of the storage electrodes are not protected due to the void V in the following blanket-etching process of the second insulating layer 13 so that the bottoms of the storage electrodes are damaged as A shown in FIG. 3.
So as to solve the problem, the method for selectively filling a photosensitive film 50 only in the inner portions of the storage electrodes instead of the second insulating layer 13, is proposed. However, when the photosensitive film 50 is filled with the inner type storage electrodes, it is difficult to control the height of the photosensitive film 50 to be equal to or lower than that of the storage electrodes. Therefore, the storage electrode has a profile of a spacer type not a plan profile as B shown in FIG. 5, after the conductive film is blanket-etched. The spacer type cylinder causes the focusing of the electric field to break the dielectric film of the capacitor. Besides, as shown in FIG. 6a and FIG. 6b, if hemi-spherical grains are formed over the inner cylinder type storage electrode having a spacer type profile so as to enhance the surface dimension of the storage electrode, the hemi-spherical grains are unstable and then detached from the storage electrode with ease. Therefore, the probability for the bridge between the storage electrodes becomes high.
It is an object of the present invention to provide a method for fabricating a semiconductor memory device for preventing the bottom of the inner cylinder type storage electrode from damaging and for obtaining the plan cylinder profile.
According to an aspect of the present invention, there is provided to a method for fabricating a semiconductor memory device, comprising the steps of: forming a first insulating layer over a substrate; etching the first insulating layer to form contact hole, thereby exposing a portion of the substrate; forming a conductive film for a storage electrode over the first insulating layer including the contact hole; forming a photosensitive film over only the conductive film within the contact hole; forming a second insulating layer over the first insulating layer to be filled in the contact hole; blanket-etching the second insulating layer and the conductive film to expose the first insulating layer, thereby forming the storage electrode; and removing the photosensitive film and the first and the second insulating layers.